The field of this invention relates to down hole screens which can be expanded into contact with the formation.
Down hole screens are used in a variety of different applications. As part of a common procedure called gravel packing, the screens are deposited adjacent the producing formation and the surrounding annular space is filled with sand known as gravel. Various fabrication techniques have been developed for manufacturing such screens and a typical example is illustrated in U.S. Pat. No. 5,611,399.
More recently it has been determined that it is desirable to reduce the size of the annular space between the screen and the formation. Reduction of the volume of the annular space around the screen discourages fluid flow along the screen which, in turn lessens the production of sand. In order to be able to produce the formation longer, it has been desirable to insert screens in well bores or laterals and thereafter expand them. A good example of the expansion techniques for a down hole screen in U.S. Pat. No. 6,012,522. In this patent, overlapping segments of screen are placed on a base pipe which is ultimately expanded from within when placed in position in the well bore or a lateral. The shortcoming of this technique is that portions of the filtering material must be moved relative to each other which subjects them to tearing which in turn can result in a failure of the expanded screen assembly to control the production of sand. Another shortcoming of such designs is the limited capacity to withstand collapse.
Other patents relating to pipe expansions are: U.S. Pat. Nos. 5,901,789 and 5,366,012.
The main objective of the present invention is to allow easy installation of the screen to the desired location followed by expansion to reduce the volume of the annular space around the screen. Yet another object of the invention is to expand the screen against the formation to entirely eliminate the annular space around it. Yet another objective of the present invention is to allow the use of the structure of the screen down hole even without expansion. Another objective of the present invention is to decrease the amount of stress on the filtration member when expanded. Yet another objective of the present invention is to provide a significantly stronger structure for the finished product which even after expansion presents a greater resistance to collapse.
Three embodiments of an expandable screen are described. In the preferred embodiment, the base layer, filtering layer, and outer layer are joined together in a sintering furnace in the form of a flat sheet which is in turn rolled up. The layered sheet is then formed into a tube by rolling it to make a longitudinal or spiral joint which is welded with connections placed on ends. In an alternative embodiment, the base layer and filtering layer are sintered together and formed into a tube which is in turn inserted into an outer protective tube. In a third embodiment, a base pipe is perforated and its exterior surface threaded. A wire runs through the threads with a protective jacket over the underlying assembly. Upon expansion, the opening sizes remain relatively constant.